Recently, in the field of magnetic disk devices represented by a hard disk drive, a high-frequency assist recording scheme has been proposed as one recording scheme that can realize a higher recording density and a higher recording capacity.
In the high-frequency assist recording scheme, a magnetic head having a high-frequency oscillator element is used, and a high-frequency magnetic field is applied to a magnetic disk. For instance, a spin torque oscillator (STO) may be the high-frequency oscillator element. By supplying a current to the STO to oscillate it, the magnetic disk device generates a high-frequency magnetic field.
In a magnetic disk device with the high-frequency assist recording scheme, methods of evaluating the oscillation characteristic of the high-frequency oscillator element have been proposed. For instance, they include a method of evaluating the oscillation characteristic of the high-frequency oscillator element by confirming resistance changes in the element. The degree of the resistance change due to the oscillation of the high-frequency oscillator element varies depending upon amount of the magnetoresistive effect of the element itself. Accordingly, it is difficult to accurately determine the oscillation characteristic of the high-frequency oscillator element. Further, since the resistance change rate is low, it is difficult to achieve a high measurement accuracy.